Chapter 2: The Integumentary System
Understand the basic structure and functions of the integument.
Become familiar with derivatives of the skin from representative clades.
Understand the evolution of the skin in a phylogenetic context.
(Ch. 2 Supplement- Figs. 2-2, 2-5, 2-12, 2-13)
The skin or
is a polyfunctional structure that plays many roles in craniates. It serves as
the outside boundary layer between an organism’s internal and external environments. It is
composed of many different tissue types and contains various structures ranging from blood vessels
to nerves. The skin performs many functions, including: providing
protection of and support for
exchange and transport of salts
, serving as a
receptor for pain and temperature
, functioning in
, serving as the basis
which can act as
or as a
, and lastly it is its
ecosystem of viruses, bacteria, fungi, yeasts, mites, and other arthropods.
Despite the multifunctional role that the skin plays, its basic structure and development are
conserved among craniates. It is composed of three main layers:
(Figures 2-1, below, and supplementary figure 2-2). The epidermis is the outermost
layer and is composed of epithelial cells that are derived from ectoderm. The epidermis rests upon a
delicate layer of fibrils termed the
. The dermis is located beneath the epidermis and
the basal lamina and is composed mainly of fibrous connective tissue derived developmentally from
mesenchymal cells. This layer contains glands and hair. The dermis is often much thicker than the
epidermis but contains far fewer cells. The hypodermis contains subcutaneous tissues including fat,
connective tissue, blood vessels, and nerves.
Typical sections of vertebrate skin showing major divisions of layers.
Adapted from Liem et al. 2001